If you visit the download page of software packages listed in the Software section of this website, you might notice terms like testing, unstable and stable. Their meaning usually depends on software companies, developers and projects. This is the scheme followed here.
Any new version is released as a testing release. Once a new bug is found, it is marked as unstable, and a new testing version is released after fixing the bugs. But if no bugs are reported after a reasonable period, the testing version is marked stable.
Notice that the version number remains the same when a testing release is marked stable or unstable.